Antimony‐Doped Tin Oxide as Transparent Back Contact in Cu2ZnSnS4 Thin‐Film Solar Cells

Abstract

Antimony‐doped tin oxide (Sn2O3:Sb, ATO) is investigated as a transparent back contact for Cu2ZnSnS4 (CZTS) thin‐film solar cells. The stability of the ATO under different anneal conditions and the effect from ATO on CZTS absorber growth are studied. It is found that ATO directly exposed to sulfurizing anneal atmosphere reacts with S, but when covered by CZTS, it does not deteriorate when annealed at T < 550 °C. The electrical properties of ATO are even found to improve when CZTS is annealed at T = 534 °C. At T = 580 °C, it is found that ATO reacts with S and degrades. Analysis shows repeatedly that ATO affects the absorber growth as large amounts of Sn−S secondary compounds are found on the absorber surfaces. Time‐resolved anneal series show that these compounds form early during anneal and evaporate with time to leave pinholes behind. Device performance can be improved by addition of Na prior to annealing. The best CZTS device on ATO back contact herein has an efficiency of 2.6%. As compared with a reference on a Mo back contact, a similar open‐circuit voltage and short‐circuit current density are achieved, but a lower fill factor is measured.